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avsprintf(): Fix a bug in usage of va_list on x86. On x86, va_list is a pointer to a single copy on the stack. avsprintf() calls lib_vsprintf() twice and so traverses the va_list twice using va_start. va_start modifies that single copy on the stack so that the second call to lib_vsprintf() fails. This appears to be an issue with x86 only so far

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This commit is contained in:
Gregory Nutt 2014-12-08 10:40:06 -06:00
parent 0354c47830
commit 297a255fd8
1 changed files with 30 additions and 3 deletions
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33
libc/stdio/lib_avsprintf.c
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@ -47,6 +47,24 @@
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* On some architectures, va_list is really a pointer to a structure on the
* stack. And the va_arg builtin will modify that instance of va_list. Since
* avsprintf traverse the parameters in the va_list twice, the va_list will
* be altered in this first cases and the second usage will fail. So far, I
* have seen this only on the X86 family with GCC.
*/
#undef CLONE_APLIST
#define ap1 ap
#define ap2 ap
#if defined(CONFIG_ARCH_X86)
# define CLONE_APLIST 1
# undef ap2
#elif defined(CONFIG_ARCH_SIM) && (defined(CONFIG_HOST_X86) || defined(CONFIG_HOST_X86_64))
# define CLONE_APLIST 1
# undef ap2
#endif
/****************************************************************************
* Private Type Declarations
@ -98,17 +116,26 @@ int avsprintf(FAR char **ptr, const char *fmt, va_list ap)
{
struct lib_outstream_s nulloutstream;
struct lib_memoutstream_s memoutstream;
#ifdef CLONE_APLIST
va_list ap2;
#endif
FAR char *buf;
int nbytes;
DEBUGASSERT(ptr && fmt);
/* First, use a nullstream to get the size of the buffer. The number
#ifdef CLONE_APLIST
/* Clone the va_list so that the contents of the input values are not altered */
va_copy(ap2, ap);
#endif
/* First, use a nullstream to get the size of the buffer. The number
* of bytes returned may or may not include the null terminator.
*/
lib_nulloutstream(&nulloutstream);
nbytes = lib_vsprintf((FAR struct lib_outstream_s *)&nulloutstream, fmt, ap);
nbytes = lib_vsprintf((FAR struct lib_outstream_s *)&nulloutstream, fmt, ap1);
/* Then allocate a buffer to hold that number of characters, adding one
* for the null terminator.
@ -131,7 +158,7 @@ int avsprintf(FAR char **ptr, const char *fmt, va_list ap)
/* Then let lib_vsprintf do it's real thing */
nbytes = lib_vsprintf((FAR struct lib_outstream_s *)&memoutstream.public,
fmt, ap);
fmt, ap2);
/* Return a pointer to the string to the caller. NOTE: the memstream put()
* method has already added the NUL terminator to the end of the string (not